Selenium deficiency in Fisher-344 rats decreases plasma and tissue homocysteine concentrations and alters plasma homocysteine and cysteine redox status

Higher blood selenium level is associated with lower risk of hyperhomocysteinemia in the elderly

BACKGROUND AND AIMS

Earlier studies have reported inconsistent association between selenium (Se) and homocysteine (Hcy) levels, while no evidence could be found from Chinese population. To fill this gap, we investigated the association between blood Se and hyperhomocysteinemia (HHcy) of rural elderly population in China.

METHODS

A cross-sectional study on 1823 participants aged 65 and older from four Chinese rural counties was carried out in this study. Whole blood Se and serum Hcy concentrations were measured in fasting blood samples. Analysis of covariance and restricted cubic spline models were used to examine the association between Se and Hcy levels. Logistic regression models were used to evaluate the risk of prevalent HHcy among four Se quartile groups after adjusting for covariates.

RESULTS

For this sample, the mean blood Se concentration was 156.34 (74.65) μg/L and the mean serum Hcy concentration was 17.25 (8.42) μmol/L. A significant non-linear relationship was found between blood Se and serum Hcy, the association was inverse when blood Se was less than 97.404 μg/L and greater than 156.919 μg/L. Participants in the top three blood Se quartile groups had significantly lower risk of prevalent HHcy compared with the lowest quartile group. When defined as Hcy> 10 μmol/L, the odds ratios and 95% confidence interval of HHcy were 0.600 (0.390, 0.924), 0.616 (0.398, 0.951) and 0.479 (0.314, 0.732) for Q2, Q3, and Q4 Se quartile groups compared with the Q1 group, respectively. When defined as Hcy≥ 15 μmol/L, the odds ratios and 95% confidence interval of HHcy were 0.833 (0.633, 1.098) and 0.827 (0.626, 1.092), 0.647 (0.489, 0.857) for Q2, Q3, and Q4 Se quartile groups compared with Q1 group.

CONCLUSIONS

Our findings suggest that higher blood Se level could be a protective factor for HHcy in the elderly.

Betaine consumption as a new clinical approach to treatment and prophylaxis of folate-related pathologies

The most important pathway in the development of folate-related pathologies is an increase in the level of homocysteine (HC). HC, a cytotoxic and neurotoxic amino acid (when its level is ≥12 μmol/L), is 1 of the most widely studied compounds in cardiology, neurobiology, oncology, and embryology for the last 20 years. Given its toxicity, the processes of endogenous detoxification of HC are of particular interest to medicine. To date, the most studied pathway is that of remethylation (the conversion of HC to methionine), with the participation of B12- and B9-dependent methionine synthase. Less studied is remethylation with the participation of the choline derivatives betaine and betaine-HC-S-methyltransferase (BHMT). Therefore, the aim of this review was to conduct a theoretical analysis of available information regarding the contribution of betaine metabolism, its enzyme, and its genetic polymorphism to folate metabolism disturbances, and the development of folate-related pathologies. This review emphasizes the potential clinical significance of 2 factors that can influence the remethylation reaction of HC: the use of betaine and identifying the BHMT gene variants and their impact on the risk for developing certain folate-related pathologies, and treatment options. Moreover, with a high level of methylation of the BHMT gene and in the presence of its low-function variants (eg, rs3733890), it is necessary to use betaine as an additional methyl donor, especially during folate therapy. More clinical research is needed to identify the effects of the different BHMT gene variants on the individual risk for folate-related pathologies to better assess the clinical significance, the need for genetic testing, and betaine consumption.

Reactive sulfur and selenium species in the regulation of bone homeostasis

Reactive oxygen species (ROS) are important modulators of physiological signaling and play important roles in bone tissue regulation. Both reactive sulfur species (RSS) and reactive selenium species (RSeS) are involved in ROS signaling, and recent work suggests RSS and RSeS involvement in the regulation of bone homeostasis. For example, RSS can promote osteogenic differentiation and decrease osteoclast activity and differentiation, and the antioxidant activity of RSeS play crucial roles in balancing bone remodeling. Here, we outline current research progress on the application of RSS and RSeS in bone disease and regeneration. Focusing on these investigations, we highlight different methods, tools, and sources of RSS and RSeS, and we also highlight future opportunities for delivery of RSS and RSeS in biological environments relating to bone.

Long-term effect of parental selenium supplementation on the one-carbon metabolism in rainbow trout (Oncorhynchus mykiss) fry exposed to hypoxic stress

This study evaluated how different forms of selenium (Se) supplementation into rainbow trout broodstock diets modified the one-carbon metabolism of the progeny after the beginning of exogenous feeding and followed by hypoxia challenge. The progeny of three groups of rainbow trout broodstock fed either a control diet (Se level: 0·3 µg/g) or a diet supplemented with inorganic sodium selenite (Se level: 0·6 µg/g) or organic hydroxy-selenomethionine (Se level: 0·6 µg/g) was cross-fed with diets of similar Se composition for 11 weeks. Offspring were sampled either before or after being subjected to an acute hypoxic stress (1·7 mg/l dissolved oxygen) for 30 min. In normoxic fry, parental Se supplementation allowed higher glutathione levels compared with fry originating from parents fed the control diet. Parental hydroxy-selenomethionine treatment also increased cysteine and cysteinyl-glycine concentrations in fry. Dietary Se supplementation decreased glutamate-cysteine ligase (cgl) mRNA levels. Hydroxy-selenomethionine feeding also lowered the levels of some essential free amino acids in muscle tissue. Supplementation of organic Se to parents and fry reduced betaine-homocysteine S-methyltransferase (bhmt) expression in fry. The hypoxic stress decreased whole-body homocysteine, cysteine, cysteinyl-glycine and glutathione levels. Together with the higher mRNA levels of cystathionine beta-synthase (cbs), a transsulphuration enzyme, this suggests that under hypoxia, glutathione synthesis through transsulphuration might have been impaired by depletion of a glutathione precursor. In stressed fry, S-adenosylmethionine levels were significantly decreased, but S-adenosylhomocysteine remained stable. Decreased bhmt and adenosylmethionine decarboxylase 1a (amd1a) mRNA levels in stressed fry suggest a nutritional programming by parental Se also on methionine metabolism of rainbow trout.

The effect of feeding adequate or deficient vitamin B6 or folic acid to breeders on methionine metabolism in 18-day-old chick embryos

Three isotopic tracers ([2,3,3-²H₃]-L-serine, [²H₁₁]-L-betaine, and [1-¹³C]-L-methionine) were administered by amnion injection into 18-day-old chick embryos to investigate the kinetics of methionine metabolism. The embryos utilized were from eggs collected from 34-week-old Cobb 500 broiler breeders that were fed either a control diet containing folic acid (1.25 mg/kg diet) and pyridoxine HCl (5 mg/kg diet) or diets devoid of supplemental pyridoxine or folic acid. Intermediate metabolites of methionine metabolism and polyamines were analyzed in 18-day-old chick embryos. There were no differences in hepatic [²H₂] methionine or [²H₃] cysteine enrichments or in physiological concentrations of sulfur amino acids for chick embryos from breeders fed the control diet and embryos from breeders fed diets containing no pyridoxine or folic acid. Supplementation of B₆ or folic acid did not affect the production of methionine and cysteine in chick embryos. However, breeders fed the control diet with both folic acid and pyridoxine supplementation produced embryos with a two-fold reduction of hepatic homocysteine and increased spermine compared with embryos from breeders fed diets containing no supplemental pyridoxine or folic acid (P < 0.05). Hepatic S-adenosylmethionine for embryos from breeders fed no supplemental B₆ was half the concentration compared with embryos from breeders fed the control diet. Embryos from breeders fed the control diet were utilized to determine the proportion of homocysteine going through remethylation and transsulfuration and also to determine the pathway of remethylation. Sixty-five percent of the methyl groups used for homocysteine remethylation from control embryos was via the MFMT pathway. Alternatively, 61% of homocysteine from control embryos was remethylated via the MFMT and the BHMT reactions and 39% of homocysteine was catabolized to cysteine via the transsulfuration pathway. These data show that in embryos, intermediate metabolites of methionine and polyamines increase in concentration when pyridoxine levels are provided in deficient concentrations to the breeder hen. In addition, this research demonstrates that folic acid deficient embryos conserve methionine, rather than catabolize it to cysteine.

Genome-Wide Association Study of Response to Selenium Supplementation and Circulating Selenium Concentrations in Adults of European Descent

BACKGROUND

Selenium (Se) is a trace element that has been linked to many health conditions. Genome-wide association studies (GWAS) have identified variants for blood and toenail Se levels, but no GWAS has been conducted to date on responses to Se supplementation.

OBJECTIVES

A GWAS was performed to identify the single nucleotide polymorphisms (SNPs) associated with changes in Se concentrations after 1 year of supplementation. A GWAS of basal plasma Se concentrations at study entry was conducted to evaluate whether SNPs for Se responses overlap with SNPs for basal Se levels.

METHODS

A total of 428 participants aged 40-80 years of European descent from the Selenium and Celecoxib Trial (Sel/Cel Trial) who received daily supplementation with 200 µg of selenized yeast were included for the GWAS of responses to supplementation. Plasma Se concentrations were measured from blood samples collected at the time of recruitment and after 1 year of supplementation. Linear regression analyses were performed to assess the relationship between each SNP and changes in Se concentrations. We further examined whether the identified SNPs overlapped with those related to basal Se concentrations.

RESULTS

No SNP was significantly associated with changes in Se concentration at a genome-wide significance level. However, rs56856693, located upstream of the NEK6, was nominally associated with changes in Se concentrations after supplementation (P = 4.41 × 10-7), as were 2 additional SNPs, rs11960388 and rs6887869, located in the dimethylglycine dehydrogenase (DMGDH)/betaine-homocysteine S-methyltransferase (BHMT) region (P = 0.01). Alleles of 2 SNPs in the DMGDH/BHMT region associated with greater increases in Se concentrations after supplementation were also strongly associated with higher basal Se concentrations (P = 8.67 × 10-8).

CONCLUSIONS

This first GWAS of responses to Se supplementation in participants of European descent from the Sel/Cel Trial suggests that SNPs in the NEK6 and DMGDH/BHMT regions influence responses to supplementation.

Ontogeny of hepatic methionine catabolic enzyme activities (Transmethylation and Transsulphuration) and associated physiological amino acids in E10-21 chick embryos and D1-49 broilers

Developmental changes in hepatic methionine adenosyltransferase, cystathionine β-synthase, cystathionase, and glycine N-methyltransferase were determined in broiler chick embryos and hatched chicks by using radiometric and spectrometric methods. Hepatic free methionine, S-adenosylmethionine, S-adenosylhomocysteine, homocysteine, cystathionine, and cysteine levels were also investigated. Results showed an increase in hepatic MAT activity from E10 to E21 during embryogenesis, suggesting greater transmethylation rates throughout the rapid embryonic growth and development period. A strong positive correlation between embryo BW and MAT activity also supports this idea. The MAT specific activity continued to increase after hatching, but there was a negative correlation between chick BW and MAT activities from D1 to D49. This may indicate different MAT isozymes exist for chick embryo hepatic tissue compared to hepatic tissue of hatched chick and growing broilers. The developmental pattern of MAT isozymes could be critical for methionine metabolism to cope with the demand imposed on the embryo, chicks, and growing broilers. Additionally, the specific activity of hepatic CBS in chick embryos was determined to be lower compared to that observed in older broilers (35 and 49 days). Since liver CBS specific activity is at the lowest point from D1-7 in young chicks, the ability to convert adequate homocysteine to cysteine through transsulphuration may be limiting for cysteine synthesis at this time. Steady-state hepatic homocysteine levels in chick embryos and chicks may be a function of the rates of homocysteine formation, remethylation, and catabolism via the transsulphuration pathway. The present study indicates young chicks from D1 to D7 may have a limited ability for adequate transsulphuration; therefore, dietary cystine may be needed for optimum performance.

Parental Selenium Nutrition Affects the One-Carbon Metabolism and the Hepatic DNA Methylation Pattern of Rainbow Trout (Oncorhynchus mykiss) in the Progeny

Selenium is an essential micronutrient and its metabolism is closely linked to the methionine cycle and transsulfuration pathway. The present study evaluated the effect of two different selenium supplements in the diet of rainbow trout (Onchorhynchus mykiss) broodstock on the one-carbon metabolism and the hepatic DNA methylation pattern in the progeny. Offspring of three parental groups of rainbow trout, fed either a control diet (NC, basal Se level: 0.3 mg/kg) or a diet supplemented with sodium selenite (SS, 0.8 mg Se/kg) or hydroxy-selenomethionine (SO, 0.7 mg Se/kg), were collected at swim-up fry stage. Our findings suggest that parental selenium nutrition impacted the methionine cycle with lower free methionine and S-adenosylmethionine (SAM) and higher methionine synthase (mtr) mRNA levels in both selenium-supplemented treatments. DNA methylation profiling by reduced representation bisulfite sequencing (RRBS) identified differentially methylated cytosines (DMCs) in offspring livers. These DMCs were related to 6535 differentially methylated genes in SS:NC, 6890 in SO:NC and 7428 in SO:SS, respectively. Genes with the highest methylation difference relate, among others, to the neuronal or signal transmitting and immune system which represent potential targets for future studies.

Anti-Oxidant and Anti-Endothelial Dysfunctional Properties of Nano-Selenium in vitro and in vivo of Hyperhomocysteinemic Rats

Purpose

Elevation of blood homocysteine (Hcy) level (hyperhomocysteinemia) is a risk factor for cardiovascular disorders and is closely associated with endothelial dysfunction. The present study aims to investigate the protective effect and underlying mechanism of nanoscale selenium (Nano-Se) in Hcy-mediated vascular endothelial cell dysfunction in vitro and in vivo.

Materials and Methods

By incubating vascular endothelial cells with exogenous Hcy and generating hyperhomocysteinemic rat model, the effects of Nano-Se on hyperhomocysteinemia-mediated endothelial dysfunction and its essential mechanisms were investigated.

Results

Nano-Se inhibited Hcy-induced mitochondrial oxidative damage and apoptosis by preventing the downregulation of glutathione peroxidase enzyme 1 and 4 (GPX1, GPX4) in the vascular endothelial cells, thus effectively prevented the vascular damage in vitro and in vivo in the hyperhomocysteinemic rats. Nano-Se possessed similar protective effects but lower toxicity against Hcy in vascular endothelial cells when compared with other forms of Se.

Conclusion

The application of Nano-Se could serve as a novel promising strategy against Hcy-mediated vascular dysfunction with reduced risk of Se toxicity.

Selenium and Epigenetics in Cancer: Focus on DNA Methylation

Chemopreventive activity of selenium (Se) may influence epigenome. In this review, we have discussed two aspects of Se and epigenetics in cancer, related to (1) the association between Se and epigenetic regulation in cancer development and prevention; (2) epigenetic modification of selenoprotein-encoding genes in different cancers. In both issues, we focused on DNA methylation as the most investigated epigenetic mechanism. The existing evidence from experimental data in human cancer cell lines, rodents, and human studies in cancer-free subjects indicates that: high Se exposure leads to the inhibition of DNA methyltransferase expression/activity; the association between Se and global methylation remains unclear and requires further investigation with respect to the underlying mechanisms and possible nonlinear character of this relationship; Se affects methylation of specific tumor suppressor genes, possibly in a sex-dependent manner; and cancer phenotype is often characterized by altered methylation of selenoprotein-encoding genes, mainly glutathione peroxidase 3.

Selenium increases hepatic DNA methylation and modulates one-carbon metabolism in the liver of mice

The average intake of the essential trace element selenium (Se) is below the recommendation in most European countries, possibly causing sub-optimal expression of selenoproteins. It is still unclear how a suboptimal Se status may affect health. To mimic this situation, mice were fed one of three physiologically relevant amounts of Se. We focused on the liver, the organ most sensitive to changes in the Se supply indicated by hepatic glutathione peroxidase activity. In addition, liver is the main organ for synthesis of methyl groups and glutathione via one-carbon metabolism. Accordingly, the impact of Se on global DNA methylation, methylation capacity, and gene expression was assessed. We observed higher global DNA methylation indicated by LINE1 methylation, and an increase of the methylation potential as indicated by higher S-adenosylmethionine (SAM)/S-adenosylhomocysteine (SAH) ratio and by elevated mRNA expression of serine hydroxymethyltransferase in both or either of the Se groups. Furthermore, increasing the Se supply resulted in higher plasma concentrations of triglycerides. Hepatic expression of glycolytic and lipogenic genes revealed consistent Se-dependent up-regulation of glucokinase. The sterol regulatory element-binding transcription factor 1 (Srebf1) was also up-regulated by Se. Both effects were confirmed in primary hepatocytes. In contrast to the overall Se-dependent increase of methylation capacity, the up-regulation of Srebf1 expression was paralleled by reduced local methylation of a specific CpG site within the Srebf1 gene. Thus, we provided evidence that Se-dependent effects on lipogenesis involve epigenetic mechanisms.

Central role of betaine-homocysteine S-methyltransferase 3 in chondral ossification and evidence for sub-functionalization in neoteleost fish

BACKGROUND

To better understand the complex mechanisms of bone formation it is fundamental that genes central to signaling/regulatory pathways and matrix formation are identified. Cell systems were used to analyze genes differentially expressed during extracellular matrix mineralization and bhmt3, coding for a betaine-homocysteine S-methyltransferase, was shown to be down-regulated in mineralizing gilthead seabream cells.

METHODS

Levels and sites of bhmt3 expression were determined by qPCR and in situ hybridization throughout seabream development and in adult tissues. Transcriptional regulation of bhmt3 was assessed from the activity of promoter constructs controlling luciferase gene expression. Molecular phylogeny of vertebrate BHMT was determined from maximum likelihood analysis of available sequences.

RESULTS

bhmt3 transcript is abundant in calcified tissues and localized in cartilaginous structures undergoing endo/perichondral ossification. Promoter activity is regulated by transcription factors involved in bone and cartilage development, further demonstrating the central role of Bhmt3 in chondrogenesis and/or osteogenesis. Molecular phylogeny revealed the explosive diversity of bhmt genes in neoteleost fish, while tissue distribution of bhmt genes in seabream suggested that neoteleostean Bhmt may have undergone several steps of sub-functionalization.

CONCLUSIONS

Data on bhmt3 gene expression and promoter activity evidences a novel function for betaine-homocysteine S-methyltransferase in bone and cartilage development, while phylogenetic analysis provides new insights into the evolution of vertebrate BHMTs and suggests that multiple gene duplication events occurred in neoteleost fish lineage.

GENERAL SIGNIFICANCE

High and specific expression of Bhmt3 in gilthead seabream calcified tissues suggests that bone-specific betaine-homocysteine S-methyltransferases could represent a suitable marker of chondral ossification.

Epigenetic effects of selenium and their implications for health

Alterations of epigenetic marks are linked to normal development and cellular differentiation as well as to the progression of common chronic diseases. The plasticity of these marks provides potential for disease therapies and prevention strategies. Macro- and micro-nutrients have been shown to modulate disease risk in part via effects on the epigenome. The essential micronutrient selenium affects human health outcomes, e.g., cancers, cardiovascular and autoimmune diseases, via selenoproteins and through a range of biologically active dietary selenocompounds and metabolism products thereof. This review provides an assessment of the current literature regarding epigenetic effects of dietary and synthetic selenocompounds, which include the modulation of marks and editors of epigenetic information and interference with one-carbon metabolism, which provides the methyl donor for DNA methylation. The relevance of a selenium-epigenome interaction for human health is discussed, and we also indicate where future studies will be helpful to gain a deeper understanding of epigenetic effects elicited by selenium.

Blood reflects tissue oxidative stress: a systematic review

We examined whether the levels of oxidative stress biomarkers measured in blood reflect the tissue redox status. Data from studies that measured redox biomarkers in blood, heart, liver, kidney and skeletal muscle were analyzed. In seven out of nine investigated redox biomarkers (malondialdehyde, reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase, vitamin C and E) there was generally good qualitative and quantitative agreement between the blood and tissues. In contrast, oxidized glutathione and the reduced to oxidized glutathione ratio showed poor agreement between the blood and tissues. This study suggests that most redox biomarkers measured in blood adequately reflect tissue redox status.

Genome-wide association study of selenium concentrations

Selenium (Se) is an essential trace element in human nutrition, but its role in certain health conditions, particularly among Se sufficient populations, is controversial. A genome-wide association study (GWAS) of blood Se concentrations previously identified a locus at 5q14 near BHMT. We performed a GW meta-analysis of toenail Se concentrations, which reflect a longer duration of exposure than blood Se concentrations, including 4162 European descendants from four US cohorts. Toenail Se was measured using neutron activation analysis. We identified a GW-significant locus at 5q14 (P < 1 × 10(-16)), the same locus identified in the published GWAS of blood Se based on independent cohorts. The lead single-nucleotide polymorphism (SNP) explained ∼1% of the variance in toenail Se concentrations. Using GW-summary statistics from both toenail and blood Se, we observed statistical evidence of polygenic overlap (P < 0.001) and meta-analysis of results from studies of either trait (n = 9639) yielded a second GW-significant locus at 21q22.3, harboring CBS (P < 4 × 10(-8)). Proteins encoded by genes at 5q14 and 21q22.3 function in homocysteine (Hcy) metabolism, and index SNPs for each have previously been associated with betaine and Hcy levels in GWAS. Our findings show evidence of a genetic link between Se and Hcy pathways, both involved in cardiometabolic disease.

Selenistasis: epistatic effects of selenium on cardiovascular phenotype

Although selenium metabolism is intricately linked to cardiovascular biology and function, and deficiency of selenium is associated with cardiac pathology, utilization of selenium in the prevention and treatment of cardiovascular disease remains an elusive goal. From a reductionist standpoint, the major function of selenium in vivo is antioxidant defense via its incorporation as selenocysteine into enzyme families such as glutathione peroxidases and thioredoxin reductases. In addition, selenium compounds are heterogeneous and have complex metabolic fates resulting in effects that are not entirely dependent on selenoprotein expression. This complex biology of selenium in vivo may underlie the fact that beneficial effects of selenium supplementation demonstrated in preclinical studies using models of oxidant stress-induced cardiovascular dysfunction, such as ischemia-reperfusion injury and myocardial infarction, have not been consistently observed in clinical trials. In fact, recent studies have yielded data that suggest that unselective supplementation of selenium may, indeed, be harmful. Interesting biologic actions of selenium are its simultaneous effects on redox balance and methylation status, a combination that may influence gene expression. These combined actions may explain some of the biphasic effects seen with low and high doses of selenium, the potentially harmful effects seen in normal individuals, and the beneficial effects noted in preclinical studies of disease. Given the complexity of selenium biology, systems biology approaches may be necessary to reach the goal of optimization of selenium status to promote health and prevent disease.

Both selenium deficiency and modest selenium supplementation lead to myocardial fibrosis in mice via effects on redox-methylation balance

SCOPE

Selenium has complex effects in vivo on multiple homeostatic mechanisms such as redox balance, methylation balance, and epigenesis, via its interaction with the methionine-homocysteine cycle. In this study, we examined the hypothesis that selenium status would modulate both redox and methylation balance and thereby modulate myocardial structure and function.

METHODS AND RESULTS

We examined the effects of selenium-deficient (<0.025 mg/kg), control (0.15 mg/kg), and selenium-supplemented (0.5 mg/kg) diets on myocardial histology, biochemistry and function in adult C57/BL6 mice. Selenium deficiency led to reactive myocardial fibrosis and systolic dysfunction accompanied by increased myocardial oxidant stress. Selenium supplementation significantly reduced methylation potential, DNA methyltransferase activity and DNA methylation. In mice fed the supplemented diet, inspite of lower oxidant stress, myocardial matrix gene expression was significantly altered resulting in reactive myocardial fibrosis and diastolic dysfunction in the absence of myocardial hypertrophy.

CONCLUSION

Our results indicate that both selenium deficiency and modest selenium supplementation leads to a similar phenotype of abnormal myocardial matrix remodeling and dysfunction in the normal heart. The crucial role selenium plays in maintaining the balance between redox and methylation pathways needs to be taken into account while optimizing selenium status for prevention and treatment of heart failure.

Epigenetic diet: impact on the epigenome and cancer

A number of bioactive dietary components are of particular interest in the field of epigenetics. Many of these compounds display anticancer properties and may play a role in cancer prevention. Numerous studies suggest that a number of nutritional compounds have epigenetic targets in cancer cells. Importantly, emerging evidence strongly suggests that consumption of dietary agents can alter normal epigenetic states as well as reverse abnormal gene activation or silencing. Epigenetic modifications induced by bioactive dietary compounds are thought to be beneficial. Substantial evidence is mounting proclaiming that commonly consumed bioactive dietary factors act to modify the epigenome and may be incorporated into an 'epigenetic diet'. Bioactive nutritional components of an epigenetic diet may be incorporated into one's regular dietary regimen and used therapeutically for medicinal or chemopreventive purposes. This article will primarily focus on dietary factors that have been demonstrated to influence the epigenome and that may be used in conjunction with other cancer prevention and chemotherapeutic therapies.

Nutritional influences on epigenetics and age-related disease

Nutritional epigenetics has emerged as a novel mechanism underlying gene-diet interactions, further elucidating the modulatory role of nutrition in aging and age-related disease development. Epigenetics is defined as a heritable modification to the DNA that regulates chromosome architecture and modulates gene expression without changes in the underlying bp sequence, ultimately determining phenotype from genotype. DNA methylation and post-translational histone modifications are classical levels of epigenetic regulation. Epigenetic phenomena are critical from embryonic development through the aging process, with aberrations in epigenetic patterns emerging as aetiological mechanisms in many age-related diseases such as cancer, CVD and neurodegenerative disorders. Nutrients can act as the source of epigenetic modifications and can regulate the placement of these modifications. Nutrients involved in one-carbon metabolism, namely folate, vitamin B12, vitamin B6, riboflavin, methionine, choline and betaine, are involved in DNA methylation by regulating levels of the universal methyl donor S-adenosylmethionine and methyltransferase inhibitor S-adenosylhomocysteine. Other nutrients and bioactive food components such as retinoic acid, resveratrol, curcumin, sulforaphane and tea polyphenols can modulate epigenetic patterns by altering the levels of S-adenosylmethionine and S-adenosylhomocysteine or directing the enzymes that catalyse DNA methylation and histone modifications. Aging and age-related diseases are associated with profound changes in epigenetic patterns, though it is not yet known whether these changes are programmatic or stochastic in nature. Future work in this field seeks to characterise the epigenetic pattern of healthy aging to ultimately identify nutritional measures to achieve this pattern.

Glucoraphanin does not reduce plasma homocysteine in rats with sufficient Se supply via the induction of liver ARE-regulated glutathione biosynthesis enzymes

Data from human and animal trials have revealed contradictory results regarding the influence of selenium (Se) status on homocysteine (HCys) metabolism. It was hypothesised that sufficient Se reduces the flux of HCys through the transsulphuration pathway by decreasing the expression of glutathione (GSH) synthesising enzymes. Glucoraphanin (GRA) is a potent inducer of genes regulated via an antioxidant response element (ARE), including those of GSH biosynthesis. We tested the hypothesis that GRA supplementation to rat diets lowers plasma HCys levels by increasing GSH synthesis. Therefore 96 weaned albino rats were assigned to 8 groups of 12 and fed diets containing four different Se levels (15, 50, 150 and 450 μg kg(diet)(-1)), either without GRA (groups: C15, C50, C150 and C450) or in combination with 700 μmol GRA kg(diet)(-1) (groups G15, G50, G150 and G450). Rats fed the low Se diets C15 and G15 showed an impressive decrease of plasma HCys. Se supplementation increased plasma HCys and lowered GSH significantly by reducing the expression of GSH biosynthesis enzymes. As new molecular targets explaining these results, we found a significant down-regulation of the hepatic GSH exporter MRP4 and an up-regulation of the HCys exporter Slco1a4. In contrast to our hypothesis, GRA feeding did not reduce plasma HCys levels in Se supplemented rats (G50, G150 and 450) through inducing GSH biosynthesis enzymes and MRP4, but reduced their mRNA in some cases to a higher extent than Se alone. We conclude: 1. That the long-term supplementation of moderate GRA doses reduces ARE-driven gene expression in the liver by increasing the intestinal barrier against oxidative stress. 2. That the up-regulation of ARE-regulated genes in the liver largely depends on GRA cleavage to free sulforaphane and glucose by plant-derived myrosinase or bacterial β-glucosidases. As a consequence, higher dietary GRA concentrations should be used in future experiments to test if GRA or sulforaphane can be established as HCys lowering compounds.

The von Hippel-Lindau (VHL) tumor-suppressor gene is down-regulated by selenium deficiency in Caco-2 cells and rat colon mucosa

To test the hypothesis that selenium affects DNA methylation and hence gene regulation, we employed a methylation array (Panomics) in the human colonic epithelial Caco-2 cell model. The array profiles DNA methylation from promoter regions of 82 human genes. After conditioning cells to repeatedly reduced concentrations of fetal bovine serum, a serum-free culture was established. Se-methylselenocysteine (SeMSC) was added at 0 (deficient Se) or 250 (control Se) nM to cells maintained in DMEM. After 7 days, cells were collected and stored at -80 °C until analysis; experiments were replicated three times. Glutathione peroxidase activity was significantly decreased in cells grown in low SeMSC. Cells grown in 250 nM SeMSC had maximal GPx activity. Genomic DNA from cells grown in the low-SeMSC media and media containing 250 nM SeMSC was incubated with methylation-binding protein followed by isolation of methylated DNA. The methylated DNA was labeled with biotin and hybridized to the methylation array. Thus, genes with promoter methylation will produce a higher chemiluminescence signal than those genes with no promoter methylation. Of the genes profiled, the von Hippel-Lindau (VHL) gene was most different as indicated by quantification following chemiluminescence detection demonstrating that the promoter region of VHL was hypermethylated in cells from the low-SeMSC media. To determine whether promoter methylation affected transcription, we isolated RNA from replicate samples and performed real-time RT PCR. VHL (mRNA) was down-regulated (fold change significantly <1) in cells grown in low SeMSC compared to cells grown in 250 nM SeMSC (control; fold change = 1). We also show that (mRNA) Vhl expression is significantly reduced in mucosa from rats fed a diet deficient in Se. Our results suggest that low Se status affects DNA promoter region methylation and that this can result in down-regulation of the tumor suppressor gene VHL.

Study of molecular targets influencing homocysteine and cholesterol metabolism in growing rats by manipulation of dietary selenium and methionine concentrations

Inconsistent results exist from human and animal studies for Se and methionine (Met) regarding their influence on homocysteine (HCys) and cholesterol (Chol) metabolism. To elucidate these contradictions, sixty-four weanling albino rats were divided into eight groups of 8, and were fed diets containing four different Se levels (15, 50, 150 and 450 microg/kg) either in combination with the recommended Met level of 3 g/kg (C15, C50, C150 and C450) or with an increased Met concentration of 15 g/kg (M15, M50, M150 and M450) for 8 weeks. Plasma HCys was twofold higher in the Se-supplemented C groups than in group C15. Met addition also doubled plasma HCys compared with the respective C groups. In contrast, the expression of the key enzymes of glutathione biosynthesis in the liver was significantly lowered by Se and in particular by Met. Liver Chol concentration was significantly higher in all the Se-supplemented C and M groups than in groups C15 and M15. Plasma Chol was, however, lowered. The uninfluenced expression of sterol-regulatory element-binding protein 2 and of hydroxymethyl-glutaryl-CoA reductase, the increased LDL receptor expression and the reduced expression of the hepatobiliary Chol exporter ATP-binding-cassette-transporter 8 (ABCG8) by Se and/or Met explain these findings. We conclude that the elevation of plasma HCys in rats by Se and Met results from a higher export into plasma. The fact that Se in particular combined with Met increases liver Chol but reduces plasma Chol should be addressed in future investigations focussing on the regulation of ABCG8, which is also selectively involved in the reverse transport of phytosterols in the small intestine.

Dietary selenium plus folic acid as an antioxidant therapy for ethanol-exposed pups

BACKGROUND

Nutrients such as folic acid and selenium are decreased in dams exposed to ethanol during gestation and lactation, affecting their metabolism, antioxidant balance, and the future health of their progeny. We will study whether the supplementation of the maternal diet with folate and selenium can prevent ethanol-induced oxidative liver disorders in the offspring.

METHODS

Dams were randomised into four groups: control, alcohol, alcohol+folic acid+Se, and control+folic acid+Se. We determined selenium by graphite-furnace atomic absorption and antioxidant enzyme activities, lipid peroxidation, and protein carbonyl by spectrophotometry in the offspring.

RESULTS

Alcohol increased serum Se levels and glutathione peroxidase (GPx) activity. However, in the liver of pups from ethanol-exposed dams a decrease in selenium was provoked and GPx activity increased with the double supplementation. Glutathione reductase (GR) and catalase (CAT) activities increased with ethanol, while double supplementation significantly decreased the GR activity. The supplemented diet reduced the protein peroxidation found in ethanol pups.

CONCLUSIONS

These results suggest that folic acid+Se could be effective in neutralising the damage of ethanol consumption in pups since it prevents peroxidation protein products.

Dietary selenium (Se) and copper (Cu) interact to affect homocysteine metabolism in rats

Previously, we reported that both Se deficiency and Cu deficiency decreased plasma homocysteine (pHcys) and increased plasma glutathione (pGSH) in rats. We also showed that the catalytic subunit of glutamate-cysteine ligase (Gclc), which catalyzes the rate-limiting step in glutathione biosynthesis, was upregulated in Se and Cu deficiencies. We suggested that in both deficiencies, Hcys was being shunted through the trans-sulfuration pathway as a result of this up-regulation. Because both Se and Cu deficiencies have similar effects, we hypothesized that a combined deficiency would exacerbate the decrease in pHcys and the increase in pGSH by further up-regulating Gclc. In a 2 x 2 experiment, male weanling Sprague-Dawley rats (n = 8-20/group) were fed an amino-acid-based diet containing either 0 or 0.2 microg Se (as selenite)/g and <1 or 6 microg Cu (as Cu carbonate)/g for 5 weeks. Our findings show that a combined deficiency of both Se and Cu results in lower pHcys and significantly elevated pGSH. However, the up-regulation of liver Gclc alone cannot explain why rats fed with the doubly deficient diet have the lowest pHcys and the highest pGSH.

Copper deficiency decreases plasma homocysteine in rats

The purpose of this study was to determine the effects of copper deficiency on key aspects of homocysteine metabolism that involve methionine recycling and transsulfuration. Male weanling Sprague-Dawley rats were fed AIN-93G-based diets containing <1 or approximately 6 mg Cu/kg. After 6 wk (Expt. 1) and 4 wk (Expt. 2) we found that plasma homocysteine was significantly decreased, and plasma glutathione significantly increased, in rats fed the low-Cu diet. Real-time RT-PCR was used to determine the expression of the subunits of glutamate-cysteine ligase (Gcl) in liver that catalyzes the rate-limiting step in glutathione biosynthesis. The expression of Gclc, the catalytic subunit of Gcl, was upregulated by Cu deficiency; Gclm, the modifier subunit, was not affected. Hepatic betaine-homocysteine methyltransferase (Bhmt), which catalyzes one of the two ways that homocysteine can be remethylated to methionine, was downregulated by Cu deficiency. Because Cu deficiency results in upregulation of Gclc and an increase in the biosynthesis of glutathione, it is plausible that the net flux of homocysteine through the transsulfuration pathway is increased. Furthermore, if Bhmt is downregulated, less homocysteine is available for remethylation (methionine recycling) and more is then available to irreversibly enter the transsulfuration pathway where it is lost. The net effect of increased Gclc and decreased Bhmt would be a decrease in homocysteine as a result of Cu deficiency.

Dietary selenium affects homocysteine metabolism differently in Fisher-344 rats and CD-1 mice

In our previous work with rats, plasma and tissue homocysteine concentrations were decreased by selenium deprivation. The purpose of this study was to follow up and expand on that work by determining the effects of selenium status (deficient, adequate, and supranutritional) on several aspects of homocysteine metabolism involving methionine recycling and transsulfuration. A 2nd objective was to determine whether there are differences in how selenium status affects homocysteine metabolism in rats and mice. Male weanling Fischer-344 rats and male weanling CD-1 mice were fed diets containing 0, 0.2, or 2.0 microg selenium (as sodium selenite)/g for 72 d or 60 d, respectively. Plasma homocysteine and cysteine were significantly decreased by feeding rats or mice the selenium-deficient diet compared with feeding adequate or supranutritional selenium. On the other hand, plasma glutathione was increased by selenium deficiency only in rats. Also, the specific activities of liver betaine homocysteine methyltransferase and glycine N-methyltransferase were decreased by selenium deficiency in rats, but were unaffected by selenium status in mice. Real-time RT-PCR was used to determine the expression of the subunits of glutamate-cysteine ligase, which catalyzes the rate-limiting step in glutathione biosynthesis. The expression of Gclc, the catalytic subunit of glutamate-cysteine ligase, was upregulated by selenium deprivation in both rat and mouse liver. Gclm, the modifier subunit of glutamate-cysteine ligase, was downregulated in rats fed 2 microg Se/g compared with rats fed adequate or deficient selenium. Based on these findings, it is evident that selenium deficiency has different outcomes in mice and rats. These variables are all related to methionine/methyl metabolism. Although only one strain of rat was compared with one strain of mouse, this work suggests that differences between species may prove vital in determining which animal model is used in studies of selenium deficiency or in studies that are designed to ascertain chemopreventive mechanisms of selenium.

Specific activity of methionine sulfoxide reductase in CD-1 mice is significantly affected by dietary selenium but not zinc

Reactive oxygen species-mediated oxidation of methionine residues in protein results in a racemic mixture of R and S forms of methionine sulfoxide (MetO). MetO is reduced back to methionine by the methionine sulfoxide reductases MsrA and MsrB. MsrA is specific toward the S form and MsrB is specific toward the R form of MetO. MsrB is a selenoprotein reported to contain zinc (Zn). To determine the effects of dietary selenium (Se) and Zn on Msr activity, CD-1 mice (N=16/group) were fed, in a 2 x 2 design, diets containing 0 or 0.2 microg Se/g and 3 or 15 microg Zn/g. As an oxidative stress, half of the mice received L-buthionine sulfoximine (BSO; ip; 2 mmol/kg, three times per week for the last 3 wk); the others received saline. After 9.5 wk, Msr (the combined specific activities of MsrA and MsrB) was measured in the brain, kidney, and liver. Se deficiency decreased (p<0.0001) Msr in all three tissues, but Zn had no direct effect. BSO treatment was expected to result in increased Msr activity; this was not seen. Additionally, we found that the ratio of MetO to methionine in liver protein was increased (indicative of oxidative damage) by Se deficiency. The results show that Se deficiency increases oxidation of methionyl residues in protein, that Se status affects Msr (most likely through effects on the selenoprotein MsrB), and that marginal Zn deficiency has little effect on Msr in liver and kidney. Finally, the results show that the oxidative effects of limited BSO treatment did not upregulate Msr activity.

Dietary selenium intake, aldehyde dehydrogenase-2 and X-ray repair cross-complementing 1 genetic polymorphisms, and the risk of esophageal squamous cell carcinoma

BACKGROUND

To the authors' knowledge, few studies have been conducted to date regarding dietary selenium and the potential gene-nutrient interactions with single-nucleotide polymorphisms (SNPs) in different pathways on the risk of esophageal cancer.

METHODS

The authors investigated the role of dietary selenium intake and its interplay with SNPs of the ALDH2 (glutamic acid [Glu] 487 lysine [Lys]) and the X-ray repair cross-complementing 1 (XRCC1) (arginine [Arg] 399 glutamine [Gln]) genes on the risk of esophageal squamous cell carcinoma (ESCC) in a population-based, case-control study in China. In total, 218 patients with ESCC and 415 healthy population control participants were interviewed. Dietary selenium intake was estimated from a food frequency questionnaire with 97 food items. ALDH2 and XRCC1 polymorphisms were detected with a polymerase chain reaction-restriction fragment length polymorphism assay.

RESULTS

The adjusted odds ratio (OR) for the highest quintile of dietary selenium intake, compared with the lowest quintile of intake, was 0.48 (95% confidence interval [95% CI], 0.25-0.89), with a strong dose-response relation (P for trend, <.01). The ALDH2 Lys and XRCC1 Gln variant alleles were associated with an increased risk of ESCC with adjusted ORs of 1.91 (95% CI, 0.96-3.80) and 1.67 (95% CI, 1.08-2.59), respectively. An elevation of the risk for ESCC was pronounced most among carriers of ALDH2 Lys/Lys and XRCC1 399Gln/Gln or Gln/Arg who consumed a low level of dietary selenium (adjusted OR, 4.16; 95% CI, 1.14-15.12).

CONCLUSIONS

To the authors' knowledge, this is the first in-depth study to suggest that genetic susceptibility may modify the association between selenium intake and the risk of ESCC. The findings indicated that individuals with low dietary selenium intake and ALDH2 Lys/Lys and XRCC1 399Gln/Gln or Gln/Arg genotypes were associated with an increased ESCC risk, especially in the presence of exposure to tobacco and alcohol carcinogens.

High serum selenium and reduced risk of advanced colorectal adenoma in a colorectal cancer early detection program

BACKGROUND

Epidemiologic and animal studies suggest that selenium may reduce risk of colorectal cancer. However, the epidemiologic data is mainly from relatively small investigations, limiting their interpretation. Although substantial evidence suggests that smoking is a strong effect modifier for other antioxidative nutrients, little is known about smoking-selenium interactions in colorectal tumors.

METHODS

We studied the association of serum selenium and advanced colorectal adenoma, a cancer precursor, in 758 cases and 767 sex- and race-matched controls, randomly selected from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Cases had at least one verified advanced adenoma (> or = 1 cm or villous elements, or high-grade dysplasia) of the distal colon, and controls had a negative sigmoidoscopy.

RESULTS

The multivariable odds ratio (OR) comparing participants in the highest quintile of serum selenium with those in the lowest quintile was 0.76 [95% confidence interval (95% CI), 0.53-1.10; P(trend) = 0.01]. The inverse association between serum selenium and advanced colorectal adenoma was significant among recent smokers (OR, 0.53; 95% CI, 0.27-1.01 for highest versus lowest tertile; P(trend) = 0.008). Serum selenium was unrelated to adenoma risk in nonsmokers and former smokers who quit smoking > or = 10 years ago.

CONCLUSION

Selenium may reduce the risk of developing advanced colorectal adenoma, particularly among the high-risk group of recent smokers.

Selenoproteins, Cholesterol-Lowering Drugs, and the Consequences Revisiting of the Mevalonate Pathway

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) and peroxisome proliferator-activated receptor alpha activators (fibrates) are the backbone of pharmacologic hypercholesterolemia and dyslipidemia treatment. Many of their clinical effects, however, are still enigmatic. This article describes how a side road of the mevalonate pathway, characterized in recent years, can rationalize a major fraction of these unexplained observations. This side road is the enzymatic isopentenylation of selenocysteine-tRNA([Ser]Sec) (Sec-tRNA), the singular tRNA to decode the unusual amino acid selenocysteine. The functionally indispensable isopentenylation of Sec-tRNA requires a unique intermediate from the mevalonate pathway, isopentenyl pyrophosphate, which concomitantly constitutes the central building block for cholesterol biosynthesis, and whose formation is suppressed by statins and fibrates. The resultant inhibition of Sec-tRNA isopentenylation profoundly decreases selenoprotein expression. This effect might seamlessly explain the immunosuppressive, redox, endothelial, sympatholytic, and thyroidal effects of statins and fibrates as well as their common side effects and drug interactions.

Oxidative stress in mothers who have conceived fetus with neural tube defects: the role of aminothiols and selenium

BACKGROUND & AIMS

Methionine metabolic impairment and selenium deficit have been associated to neural tube defects. The relationship between thiol metabolism and selenium is not well known. We assessed the status of aminothiols and selenium, as well as thiolic status and the amino acids involved in arginine synthesis in the case of selenium depletion and repletion, studying their relationship to neural tube defects.

METHODS

We studied 44 women of 37 +/- 8 years (mean +/- SD) who had conceived fetuses with neural tube defects as cases; and 181 women of 39 +/- 7 years (mean +/- SD) with healthy children as controls. We determined selenium, vitamin B12, serum folates, plasma thiol compounds and amino acids. Homocysteine transsulfuration was assessed using total cysteine/total homocysteine ratio (tCys/tHcy), and selenium repletion cut-off value was 1.06 micromol/l (84 microg/l).

RESULTS

Cases showed significantly lower levels (median) than controls of total homocysteine (P = 0.001), total cysteinylglycine (P < 0.001), selenium (P < 0.001) and tryptophane (P = 0.002); and higher tCys/tHcy levels (P < 0.001), glutathione (P = 0.008) and L-arginine (P = 0.001). Cases with selenium depletion (selenium < or = 1.06 micromol/l) had significantly higher levels than controls of cysteine (P = 0.010), glutathione (P = 0.005), tCys/tHcy (P < 0.001), and arginine (P = 0.004), but significantly lower levels than controls of tryptophane (P = 0.027), cysteinylglycine (P < 0.001) and folates (P < 0.001). Only cysteinylglycine was lower than controls (P < 0.001) when selenium > 1.06 micromol/l. Methionine levels were higher in cases with selenium depletion than in repletion (P = 0.029).

CONCLUSIONS

According to our data, a diet deficient in selenium and folates or their absorption impairment, and/or other mechanisms related to polyamines and nitric oxide can lead to oxidant/antioxidant imbalance and to a higher occurrence of these malformations.

Serum selenium is associated with plasma homocysteine concentrations in elderly humans

Low selenium levels in humans have been associated with several pathologies; however, an earlier animal investigation found a direct association between Se intake and total plasma homocysteine (tHcy) concentrations. To date, the importance of serum selenium levels in association with tHcy in humans has not been determined. We evaluated the cross-sectional association of blood selenium concentrations with plasma tHcy and other determinants of this cardiovascular disease risk factor. We estimated protein intake and measured the blood status of selenium, tHcy, and several other related factors in serum such as folate, vitamin B-12, and creatinine. Serum selenium was inversely associated with tHcy, explaining 5.8% of tHcy variance with respect to 2.2% accounted for by serum folate. Furthermore, there was a 63% decreased risk of higher tHcy concentrations (>14 micro mol/L) for subjects with serum selenium in the highest tertile (P = 0.013). We also found an inverse association of protein intake with tHcy in men (beta = -0.144; P = 0.036), which disappeared after controlling for serum Se concentrations (beta = -0.055; P = 0.003). In conclusion, selenium should be considered as a potential factor to lower tHcy. In addition, the described association between protein intake and homocysteine levels could be mediated by this trace element.

Dietary folate and selenium affect dimethylhydrazine-induced aberrant crypt formation, global DNA methylation and one-carbon metabolism in rats

Several observations suggest a role for DNA methylation in cancer pathogenesis. Although both selenium and folate deficiency have been shown to cause global DNA hypomethylation and increased cancer susceptibility, the nutrients have different effects on one-carbon metabolism. Thus, the purpose of this study was to investigate the interactive effects of dietary selenium and folate. Weanling, Fischer-344 rats (n = 23/diet) were fed diets containing 0 or 2.0 mg selenium (as selenite)/kg and 0 or 2.0 mg folate/kg in a 2 x 2 factorial design. After 3 and 4 wk of a 12-wk experiment, 19 rats/diet were injected intraperitoneally with dimethylhydrazine (DMH, 25 mg/kg) and 4 rats/diet were administered saline. Selenium deficiency decreased (P < 0.05) colonic DNA methylation and the activities of liver DNA methyltransferase and betaine homocysteine methyltransferase and increased plasma glutathione concentrations. Folate deficiency increased (P < 0.05) the number of aberrant crypts per aberrant crypt foci, the concentration of colonic S-adenosylhomocysteine and the activity of liver cystathionine synthase. Selenium and folate interacted (P < 0.0001) to influence one-carbon metabolism and cancer susceptibility such that the number of aberrant crypts and the concentrations of plasma homocysteine and liver S-adenosylhomocysteine were the highest and the concentrations of plasma folate and liver S-adenosylmethionine and the activity of liver methionine synthase were the lowest in rats fed folate-deficient diets and supplemental selenium. These results suggest that selenium deprivation ameliorates some of the effects of folate deficiency, probably by shunting the buildup of homocysteine (as a result of folate deficiency) to glutathione.

Selective induction of liver parenchymal cell heme oxygenase-1 in selenium-deficient rats

Liver heme oxygenase (HO) activity is higher in selenium-deficient rats than in control animals under basal conditions and is further increased in them, but not in controls, by phenobarbital treatment. In the present study we characterized liver HO induction by selenium deficiency using molecular methods. Severe selenium deficiency in rats caused a doubling of liver HO activity without affecting spleen, kidney, brain, or testis HO activities. HO-1 protein and mRNA were increased to accompany the increased HO activity, but HO-2 protein and mRNA were not increased. Fractionation of the liver into hepatocyte and Kupffer cell/endothelial cell fractions revealed that the increased HO activity resides in the hepatocyte fraction. Immunohistochemical localization of HO-1 protein confirms the induction of HO-1 taking place solely in hepatocytes and throughout the liver lobule. Phenobarbital treatment sharply increased HO-1 mRNA and protein expression in selenium-deficient liver and HO activity in hepatocytes, but had no effect in control liver or in the Kupffer cell/endothelial cell fraction of selenium-deficient liver. Electrophoretic mobility shift assays showed increased AP-1 binding activity, suggesting an involvement of this redox-sensitive transcription factor in the induction by phenobarbital of HO-1 in selenium deficiency. We speculate that selenium deficiency affects hepatic antioxidant selenoproteins, resulting in an up-regulation of HO-1.

Selenium supplements do not increase plasma total homocysteine concentrations in men and women

Studies in rats indicate that plasma total homocysteine (tHcy) is decreased in selenium deficiency and increases with selenium supplementation. The aim of this study was to determine the effect of selenium supplements on plasma tHcy concentrations in a population that has suboptimal selenium status. Subjects from Dunedin, New Zealand (n = 189) were randomly assigned to receive a supplement containing 200 micro g selenium or placebo for 20 wk. At baseline, 67% (n = 112) of the participants had plasma selenium concentrations < 1.2 micro mol/L, a concentration believed to be that necessary for full glutathione peroxidase (Gpx) activity. At 20 wk, plasma selenium concentration and Gpx activity increased in the selenium group by 1.2 micro mol/L [95% confidence interval (CI): 1.1, 1.3] and 5.1 nkat/g protein (3.7, 6.5), respectively, changes that were significantly greater than the changes in the placebo group (P < 0.001). At 20 wk, mean changes in plasma tHcy concentrations were 0.1 micro mol/L (95% CI: -0.4, 0.5) and -0.2 micro mol/L (-0.7, 0.3) in the supplemented and placebo groups, respectively, compared to baseline. There was no difference in the mean changes in plasma tHcy between the supplemented and placebo groups (P = 0.54). These results suggest that selenium supplementation does not influence plasma tHcy concentrations in healthy populations in developed countries, whose selenium status is characterized by lower plasma selenium concentrations.

The antioxidant role of selenium and seleno-compounds

Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and gamma-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO(4)) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G(2)-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G(1) phase and cell death was predominantly induced by apoptosis.